Introversion vs Extraversion

Introversion and extroversion are probably two of the most widely known personality traits. Stereotypically, an introvert is characterised by someone who is quiet and shy, and prefers to spend time alone. In contrast, an extrovert is usually loud and boisterous, and always needs to be surrounded by people.

The words extrovert and introvert were first popularised almost 100 years ago by Carl Jung in 1921. Introverts prefer the inner world and to focus on their thoughts, whereas extroverts prefer the external world of activities and other people. Introverts also gain their energy from being alone, whereas extroverts recharge by socialising with others.

In modern society, it is extroverts who are praised and rewarded; being called ‘quiet’ is often a negative adjective. In her book ‘Quiet’, Susan Cain explores why the extrovert has become the ideal, and made me realise that there is far more to introversion and extroversion than the stereotypes described above.

For example, Cain describes introversion and extroversion as opposing ends of a scale. People can be firmly at one end, but they can also be somewhere in the middle – known as ambiversion. People can also be extremely different depending on their current situation, with introverts who normally prefer peace and quiet able to enjoy performing on stage in front of thousands. This is characterised by the “person-situation” debate in psychology – are personality traits fixed, or do they just depend on the situation that the person is in? Psychologists on the “person” side argue that we have fixed personality traits which are based on our biology, whilst those on the “situation” side believe that we do not have core traits, but a range of traits which we exhibit in certain situations.

One psychologist in favour of the “person” side of the debate is Hans Eysenck, who developed his personality theory around levels of stimulation – the amount of input we are receiving from external factors. He used this to explain introverts and extroverts, with extroverts preferring higher levels of stimulation than introverts, and so seeking it through spending more time in social situations. The amount of stimulation you prefer has a biological basis, with Eysenck hypothesising that an area of the brain known as the ARAS (see image below) involved is in controlling the balance of stimulation. He believed that the ARAS functioned differently in introverts and extroverts, which is why extroverts seek stimulation, whilst introverts retreat from it (Eysenck, 2017).


Although psychologists now think that things are a bit more complicated that Eysenck’s theory, there is some evidence to suggest the basis of it is true. In one of his famous experiments, he put a drop of lemon juice on the tongues of introverts and extroverts and measured the amount of saliva they produced (which showed how stimulating they found the juice). He found that introverts produced more saliva to this stimulus, as they are more sensitive to stimulation (Eysenck & Eysenck, 1967). Another study asked introverts and extroverts to take part in a task whilst wearing headphones which randomly played bursts of noise. Participants were asked to set the level of this noise to what was most comfortable for them, and results showed introverts set this level at an average of 55 decibels, compared to 72 decibels for the extroverts. When introverts had to do the task with the same noise level as the extroverts (or vice versa) they performed much worse, despite their performance being equal before (Geen, 1984).

Research such as this suggests there is a biological basis to whether we are more introverted or extroverted. Which category do you think you would best fit in to?

Thanks for reading and if you want to find out more about this topic I’d definitely recommend reading Susan Cain’s book – referenced below.

References – as mentioned in Cain, 2013:

Cain, S., 2013. Quiet: The power of introverts in a world that can’t stop talking. Broadway Books.

Eysenck, S.B. and Eysenck, H.J., 1967. Salivary response to lemon juice as a measure of introversion. Perceptual and motor skills24(3_suppl), pp.1047-1053.

Eysenck, H., 2017. The biological basis of personality. Routledge.

Geen, R.G., 1984. Preferred stimulation levels in introverts and extroverts: Effects on arousal and performance. Journal of Personality and Social Psychology46(6), p.1303.

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